Macro b_tree_map

macro_rules! b_tree_map {
    () => { ... };
    ($($key:expr => $val:expr),*) => { ... };
}

A macro to create a new BTreeMap, providing two usage options:

1. b_tree_map!() - Creates an empty BTreeMap.
2. b_tree_map!(key1 => value1, key2 => value2, ...) - Creates a BTreeMap containing the specified key-value pairs.

Examples:

use std_macro_extensions::*;
let empty_map: BTreeMap<i32, i32> = b_tree_map!();
let populated_map = b_tree_map!(
    "key1" => 1,
    "key2" => 2,
    "key3" => 3
);

BTreeMap is an ordered map that allows iteration over keys in their sorted order. This macro simplifies the process of creating BTreeMap, improving code readability and maintainability.